models of the atom Flashcards
what did JJ Thompson discover? Explain what was his model.
JJ Thompson discovered the existence of electrons. His model was the plum pudding model, which was that the atom was a positively charged sphere with negative electrons scattered within.
what did Ernest Rutherferd do? Describe the experiment that was carried out.
he replaced the plum pudding model with the nuclear model when he carried out the Alpha scattering experiment
the alpha scattering experiment was when a beam of alpha particles (positive charge) were directed at a very thin gold leaf suspended in vaccum
why was the gold foil surrounded by a vaccum? And why was gold used?
the vaccum was used because any deflection of the alpha particles would only be because of collisions with the gold foil and not due to deflections of anything else.
gold was used because its the only material that could be rolled out very thin without cracking
what were the results of the Alpha scattering experiment?
-most of the alpha particles did pass through the foil
-a small number of alpha particles were deflected by large angles
-very small number bounced straight back
what were the conclusions after the results of the alpha scattering experiment?
- The fact that most alpha particles passed straight through meant that the atom was mostly empty space
- A small number being deflected back by large angles meant that there is a concentration of positive charge in the atom.
- T he very small amount of alpha particles that were deflected straight back suggested that the positive charge and mass in the atom are concentrated in a tiny volume ( the nucleus )
what did Niels Bohr discover?
the existence of electrons in energy levels-When atoms absorb energy, the electrons at a particular level are pushed up to higher levels (at bigger distances from the nucleus). In time, they jump back down to a lower level releasing light of definite frequencies.
what did James Chadwick discover?
the neutron
